Polychlorinated biphenyls (PCBs) and the DDT/DDE (DDE is the stored metabolite of DDT) family are toxic, widespread pollutants. Both pass from mother to child through the placenta and by contaminating breast milk. This project included a study of subjects exposed to low levels of both compounds in North Carolina, a study in Mexico where levels of DDE are two to five times higher, and a study of persons poisoned by PCBs in Taiwan. PCBs and DDE can cause long-term induction of drug and steroid metabolizing enzymes in animals. In North Carolina, we are planning to look at onset of puberty in a cohort of children we have followed since 1978. In Mexico, in a preliminary analysis, we found women who have higher levels of DDE in breast milk have shorter lactations. This is similar to what we found previously in North Carolina, and may be a result of the estrogenicity of o,p-DDE, since estrogens decrease milk volume. In Taiwan, an epidemic of 2000 cases of PCB poisoning occurred in 1979. We are planning a study of mortality in the cohort at twelve years of follow-up. We have also found that the severity of the cognitive delay and behavioral disorder seen in children born to poisoned mothers does not diminish with the amount of time between the poisoning and the child's birth, nor does it decrease as the child gets older.